Experimental study of stable propagation and efficient electron acceleration in plasmas with ultra-short laser pulses

In this thesis experimental activities concerning the interaction of high-intensity, ultra-short laser pulses with gas-jet and plasmas, aimed to study the propagation and the production of high-energy electrons through wakefield processes are presented. The effects of propagation of the UHI10 10 TW, 65 fs laser pulse operating at CEA of Saclay (France) in presence and in absence of the pre-plasma produced by its Amplified Spontaneous Emission nanosecond pedestal has been investigated. The presence of the pre-plasma contribute to a spatial filtering of the crossing pulse, while its propagation in absence of the pre-plasma is affected by a series of non-linear effects in the external spatial region of the pulse. The ASE pedestal is found to possibly create favorable conditions in laser wakefield acceleration of electrons by creating pre-formed plasma channels able to optically guide the fs pulse. Experimental conditions in which relativistic electrons are efficiently generated have been found and characterized in a second experiment carried out with the same UHI10 laser and a supersonic helium nozzle. Several diagnostics have been independently employed to monitor the plasma key parameters and the electron signal. The data analysis shows the consistence of the obtained results. Electron bunches with energies in the range 10-45 MeV and high-charge have been efficiently accelerated even over several days of data-taking. Such particles can be used for many nuclear applications as well as seed for external injection acceleration experiments. The correlation between electron energy and gas-delivering nozzle diameter has been studied also with the aid of a modeling of the experiment via numerical simulations. At last, the use of a laser-plasma based electron accelerator for medical treatment of tumors and for nuclear studies has been considered and discussed.